Relay system



March 9, 1934. A. H. LAMB 1,949,689

RELAY SYSTEM Filed May 7, 1932 (LA ,go wg Fatentecl Mar. 6, 1934 UNITEDSTATES PATENT oFFicE RELAY SYSTEM Application May '7, 1932, Serial No.609,911

9 Claims.

This invention relates to relay systems and particularly to a systemadapted to control the closing and opening of an electric circuit inaccordance with the intensity of stimuli which are g'subject to minorfluctuations that, if not compensated for, would cause chattering of theclosure means for the circuit which is to be controlled.

In the application of relay systems for coniotrolling the closing ofelectric circuits to service wherein the intensity of the stimulus issubject to minor fluctuations, such as where a relay circuit is employedto energize a light source in accordance with the intensity ofillumination at lt' a predetermined point, certain difficulties havebeen encountered.

An object of the present invention is the provision of a relay system,responsive to a stimulus of predetermined intensity to energize aneleczfltric circuit, which system is effective to energize the circuitonly when the intensity of the stimulus obtains a predetermined valuefor a predetermined period of time. Another object of the invention isthe provision of a relay sys- Zii-tem for energizing a source of light,such as that employed for flood lighting, advertising signboards orsimilar uses, wherein the light source is energized when the intensityof illumination at a predetermined point decreases to a predeterminedvalue and for deenergizing the source when the intensity increases tothe same, or another, predetermined value, which system is er"- iectiveto energize or deenergize the source only when the critical value ofillumination is main tained for a predetermined period of time.

Another object of the invention is to provide a simple and reliablerelay system of the stated type which is sensitive to relatively slightvariations in the actuating stimulus but which operates 49 to close themain circuit only when the intensity or" the stimulus remains below apredetermined value for a predetermined proportion of a predeterminedperiod of time.

These and other objects of the invention will appear from the followingdescription taken with the accompanying drawing, wherein:

Fig. 1 illustrates diagrammatically a relay system embodying theinvention, and

Fig. 2 is a fragmentary view showing a modi- 59 fication.

A light-sensitive element 1, such as a photoelectric cell, is disposedat the point at which the illumination or light intensity is to controlthe operation of the relay system. The cell 1 is connected to the movingcoil 2 of a sensitive relay 3 having a contact arm 4 movable between twocontacts 5, 6. The contact arm 4 of relay 3 is biased towards thecontact 5 and will be held away from that contact only so long as thecurrent from the cell 1 exceeds a predetermined 4 value, and will hemoved into engagement with contact 6 only when the current outputreaches a somewhat higher and predetermined value. Contacts 5, 6 areconnected to the relay terminals 7, 8, respectively, and the contact arm4 is connected to a terminal 9.

The relay 3 is connected to a thermal interlocking relay 10 which closesand opens a circuit including a pair of conductors ll, 12 to which aload or power relay 13 is connected.

The interlocking relay 10 has a pair of cooperating main contacts 14, 15constituting a main switch 16, one contact 15 being connected to thepower relay conductor 11 and the other contact 14 being carried by andelectrically connected to 7 the bimetallic strip 17, that is, in turn,connected to the relay terminal 9.-

The arm 17 also carries an auxiliary contact 18 electrically connectedthereto and disposed for engagement with a stationary contact 19 to forman auxiliary switch 20. At normal temperature, the bimetallic strip 1'?is so positioned that both sets of contacts controlled thereby are open,and the contacts i l, 18 are so arranged that the auxiliary switch 26closes before the main switch 16 when the bimetallic strip 1'7 isdeflected by an increase in temperature.

The stationary contact 19 of the auxiliary switch 20 is connected to asecond thermally-responsive contact strip 21 that, at normaltemperatures, holds its contact 22 in engagement with a cooperatingstationary contact 23. These contacts form a second auxiliary orthermally controlled switch 2 or" which the stationary contact 23 isconnected to the terminal '7 of relay 3.

A heater coil 25 for bimetallic strip 17 is connected between theterminals 7 and 9 of relay 3 through a source of current, such as abattery 26, and a heater coil 27 for bimetallic strip 21 is similarlyconnected, through battery 26, between terminals 8 and 9 of relay 3.

A separate source of current may be provided for energizing the powerrelay 13 upon the closing of the main switch 16 but, as illustrated, thebattery 26 is employed to actuate the relay 13 by connecting the lead 12or" the power relay to the lead extending from source 26 to the heatercoils.

As shown in the fragmentary view, Fig. 2, which represents analternative form of that portion of the Fig. 1 circuit which lies to theright of the broken line, the power relay 13 may be omitted when theload, shown as a bank of lights 28, is of such magnitude that it may beoperated directly from the current source 26.

The operation of the system is as follows:

It the intensity of the light falling upon the cell 1 is betweenpredetermined critical values, the several switches will assume thepositions shown in Fig. 1. When the intensity of illumination decreasesbelow the lower critical value, the current through the circuit whichincludes the cell 1 and moving coil 2 decreases to such a value that thearm 4 rotates into engagement with the contact 5, thus completing acircuit through the battery 26 and the heating coil 25.

If the intensity of illumination remains below the lower critical valuefor a predetermined period of time, the arm 17 is heated and deflectedby the current flow through coil 25 to bring the contact 18 intoengagement with the contact 19. A circuit in parallel with the contacts4, 5 is thereby completed through battery 26 and heater coil 25 by thearm 17, the auxiliary switch 20, the second arm 21 and second auxiliaryswitch 24. This circuit serves as a holding circuit for the heater coil25 for the reason that, even if the illumination increases to a valueabove the lower critical value and the relay contacts 4 and 5 areopened, the coil 25 will be energized.

As the current flow through the coil 25 continues to heat the arm 17,the latter is still further deflected until the contacts 14 and 15 arebrought into engagement to close the main circuit connecting theconductors 11 and 12, thus energizing the load line that is controlledby the power relay 13.

This condition obtains until the illumination at cell 1 increases tosuch magnitude that the contact arm 4 of the sensitive relay 3 is movedinto and held in engagement with contact 6 for such a period thatcurrent flow through the heater coil 2'7 deflects the bimetallic strip21 to open contacts 22, 23 of the auxiliary switch 24 of the holdingcircuit. This interruption of current flow through coil 25 and theconsequent cooling of the bimetallic strip 17, separates the contacts 14and 15, thus deenergizing the load relay 13 to open the load circuit.

As will be apparent from the foregoing, although the light-sensitiveelement 1 is so aiiected by shadows and other variations in theillumination falling thereon, as to actuate the relay 3, theinterlocking relay 10 is not active to close the main switch 16 untilthe relay 3 has been closed a surficient proportion of a predeterminedperiod for the heating coil 25 to heat the arm 1'? to effect movement ofthe contact 18 into engagement with the contact 19. If, after thisauxiliary switch 20 is closed, the illumination increases above thecritical value, the switch 20 will not be opened since the holdingcircuit through the second thermal switch 24 does not include the relay3. Similarly, the power relay 13 will not be opened when the lightintensity increases to bring contact arm 4 into momentary engagementwith contact 6, but remains closed until current flow through heatercoil 27 persists for such time as to open the auxiliary switch 24.

It should be obvious that the relay system herein disclosed is capableof other applications than the one disclosed. The light sensitiveelement may be replaced by any element which is responsive to a variablestimulus which it is de-- sired to have control the closing and openingof a circuit, such as temperature, humidity 01 other analogous variablestimuli. A sensitive relay and an interlocking delay relay of thedescribed type may therefore be used to prevent chattering in systems inwhich a load circuit is controlled by other factors which may be subjectto short period fluctuations.

I claim:

1. The combination with a load circuit and a relatively sensitivecontrol relay, of relay means for energizing said load circuit only whensaid control relay is closed for a predetermined period of time, saidmeans comprising a thermally-responsive main switch in said loadcircuit, actuating means for said switch including said control relayand a heating coil, means independent of said control relay formaintaining the energization of said heating coil, and means includingsaid control relay for rendering inoperative said maintaining means.

2. In a relay system, the combination with a sensitive relay actuated bychanges in the magnitude of a variable quantity, and a load circuit tobe controlled from said sensitive relay, of an interlocking relayinterposed between said sensitive relay and load circuit, saidinterlocking relay including a main switch for controlling said loadcircuit, a heat-responsive actuating means for said main switch, acircuit controlled by said sensitive relay and including a coil forheating said actu ating means, means operative upon the flow of currentthrough said coil for a predetermined period to close a holding circuitthrough said coil independently of said sensitive relay, heat-responsivemeans for opening said holding circuit, and a second circuit controlledby said sensitive relay and including a coil for actuating said secondheat-responsive means.

3. The combination with a load circuit and a relatively sensitivecontrol relay, of relay means for energizing said load circuit only whensaid control relay is closed for a predetermined period of time, saidmeans comprising a main switch for closing said load circuit, anactuating coil for said main switch, a circuit including said coil andsaid control relay, a holding circuit for said coil, a holding switchoperable to closed position by the actuating coil of said main switch,the contacts of said holding switch being in said holding circuit andadapted to engage prior to the closing of said main switch, an auxiliaryswitch in said holding circuit, an actuating coil for said auxiliaryswitch, and a circuit including said second actuating coil and saidcontrol relay.

4. In a relay system, the combination with means for alternativelyclosing one of two circuits, of a relay having two main circuitscontrolled by said means, each of said circuits including a source ofcurrent and the heating coil of a thermally responsive switch actuator,a main switch and an auxiliary switch controlled by the first of saidactuators, a second auxiliary switch controlled by said second actuator,and a holding circuit including said auxiliary switches in series forsupplying current to the heating coil of said first actuatorindependently of said circuit closing means.

5. The combination with a relay including a contact arm movable betweentwo contacts, a circuit between the contact arm and each contact,

a source of current and a heating coil in each 1 of said circuits, aheat-responsive strip positioned adjacent each heating coil to receiveheat energy from the respective coils, the first of said strips carryinga pair of contacts, a holding circuit for supplying current to theheating coil of said first strip, said holding circuit including astationary contact cooperating with one of said strip contacts, andswitch means controlled by said second strip for opening said holdingcircuit when current is supplied to said second heating coil for apredetermined period.

6. In a relay system for controlling the energization of an electriccircuit, the combination with a load circuit, and a two position relayfor alternatively closing one of two circuits, of heating coils and asource of current in each of said circuits, a thermally responsive mainswitch actuated by one of said coils, and means for closing a holdingcircuit to supply current to the heating coil of said main switch, saidmeans including auxiliary switches serially connected in said holdingcircuit and actuated by the respective heating coils, the auxiliaryswitch actuated by the heating coil of said main switch being open atnormal temperatures and the second auxiliary switch being closed atnormal temperatures, whereby the energization for a predetermined periodof the relay circuit including the heating coil of said main switchefiects the closing of the auxiliary switch associated therewith andthereby completes the holding circuit.

'7. The invention as set forth in claim 6, wherein the contacts of themain switch and the auxiliary switch associated therewith are positionedto effect closure of said main switch subsequent to the closure of itsassociated auxiliary switch.

8. In a relay system for controlling a load circuit in response tovariations in light intensity, a light-sensitive device, a sensitiverelay included in circuit with said device and having a contact armmovable into engagement alternatively with one of two contacts when thelight intensity reaches predetermined higher and lower values, circuitsincluding a source of current and a heating coil connected between thecontact arm and the respective contacts, a heat-responsive stripadjacent the first of said coils and carrying the movable contacts of amain switch and of an' auxiliary switch, a stationary contactcooperating with the movable contact of said auxiliary switch forclosing a holding circuit through the said first coil independently ofsaid relay contacts after current flow through the said first coil heatssaid strip to a predetermined temperature, a heat-responsive stripadjacent the second of said heating coils, and a switch in said holdingcircuit and controlled by said second heat-responsive strip, said lastswitch being normally closed and being actuated to open position by theflow of current through said second heating coil.

9. The invention as set forth in claim 8 wherein the stationary contactof said main switch is positioned to be engaged by its movable contactonly after the said strip is heated to a higher temperature than thateffective to close said holding circuit.

ANTHONY H. LAMB.

